Process for the preparation of light-sensitive emulsions



Patented Nov. 28, 1939 UNITED STATES PATENT OFFICE PROCESS FOR THE PREPARATION OF LIGHT-SENSITIVE EMULSIONS 'Carl Adolf Schleussner, 'Frankfort-on-the-Main,

Germany No Drawing. Application March 23, 1936,Serial No. 70,541. In Germany March 22, 1935 4 Claims.

(Granted pared by mere heating, and only involve'a considerably increased. expenditure. 4

It has now been found however eiiect is obtained by submitting the photographic emulsions during one or more of the various stages of their treatment to electrical; electromagnetic or mechanical oscillations of' varying size with simultaneous cooling,'so that the 2temperature at which-the treatment of the emulsions is carried out is less than that formerly employed for photographic emulsions. Electrical high frequency oscillations-suchas are used in short wave diathermy, short broadcasting waves and sound waves are examples of oscillations which may be used'according to the present in-.

vention. In the Ausfiihrlichen Handbuch der Photographic" Volume:1II, Part I,'oi Dr. Ing. Fritz Wentzel, Halle 1930, published by Wilhelm Knapp, is described the present position as regards the preparation of emulsions. Referenceis made first of all 'to page 107 of this publica-' tion where it is said that differences in ripeness are caused finally also by the fact that certain portions ofthe emulsion such as that portion near the wallsoi the vessel receive a different amount of heating from those in the middle of thevessel. Difierences in the ripeness of an emulsion cannot be prevented by careful cm? tinual stirring during the admixing.

Moreover on page 102, it is stated? It the water and gelatine content of an emulsion is reduced by too great an amount. very sensitive silver bromide is certainly formed easily, but the of aconcentrated silver nitrate solution with a concentrated, solution of abromine salt gives a coarse and grainy emulsion of.popr pho.'

tographic properties, and, as has already been mentioned. too-much silver bromide settles out because, oi. the-imperfect carrying powers of the aelatine.

that a special and halide salts, or during a subsequent stage under the provisions of sec. .14, act of March 2, 1927; 3 5'7 0. G.

'tration at which the formation of silver bromide takes place by 50%, and, what is more, to reduce the gelatine content by 50% or over as compared with normal emulsions, without any curling up or the formation 'of a coarse and grainy emul- 5 sion. The especial; advantages of this process accordingly consist in the fact that at lowerv temperatures the treatment. can be carried out with higher concentrationslof silver bromide and lower concentrations of gelatine without any 're-' 10 sultant fog or sediment appearing in the emulsion. The effectcan be still more increased by the addition to theremulsion of substan esjwhich have no chemical action upon the' emu ion, but.

which increase the activity of the oscillations. Examples of the materials which are suitable in this connection are colloidal silver, fineglass beads or glass dust.

The treatment of the emulsion with oscillations according to the presentinvention may be carried outduring any stage in the prepara- 9 tion of this emulsion for use, for example dur- 'ing the cold-ripening step; if such be employed, during the period of interaction of the silver in the preparation. The amount of artificial cooling will thenbe sochosen that a temperature appropriate to the particular stage in the a preparation is maintained. Preferably, however,

the emulsion is treated with theoscillations throughout the whole'of its preparation.

The process according to the invention is explained more precisely by the one example hereafter:

An emulsion or the normal kind with 600 gms. of silver, as usually employed in the photographic .emulsion art, was treated by three parallel tests as follows, I a a (1) Emulsifled, digested'and redigestedat 40?" C. by warming with hot, water.

(2) Treated atj40 C. by warming with trical oscillations. a f(3) Treated with electrical oscillatory energy and submitted to simultaneous cooling .with

water at a temperature of 15 0., whereby the emulsifying, digestion and 'redigestion took place at,.38 C. f

The remaining chemical and other experimen tal conditions were the same in every respect v in all three experimen'ts. The oscillations were'so supplied to the-emulsion by means of an emitter and their wavelength was 100 metres.

The emulsions prepared as indicated above were treated and-run-in by the usual methods.

Examination of the resultant products by the DIN'method gave the following: 1

Experiment ,1 16/10 DIN 0.3 Fog Experiment 2 16/10 DIN 0.3 Fog Experiment 3 -18/10 DIN 0.2 Fog The solubility and the flne granulation were tested by a screening method. The results are given below, the solubility being greater, the smaller the corresponding number.

Experiment 1 gave the numeral value 5. Experiment 2 gave the numeral value 5. Experiment 3 gave the numeral value 3-4.

Moreover Experiment 3 gave a 10% better yielq from the same quantity of silver, in spite oi the smaller tog density as compared with Experiments 1 and 2. From this it is apparent that the decommately 100 meters wave length and in the neigh-' I borhood of 38 C. is critical to this process.

WhatI claim is: 1. A method of preparlnga photographic emulsion comprising treating the emulsion with oscillations of approximately 109 meters wave length thus tending to produce a substantial increase in temperature of the emulsion, and artificially cooling the emulsion during said treatment to main tain theemulsion at a substantially constant temperature at about 38 C.

2. A method of improving photographic emulsions' comprising adding glass beads to the emulsion, exposing the emulsion to oscillations of approximately 100 meters wave length, thus tending to produce a development of heat, and maintaining the temperature ofemulsien substantially constant by cooling at about 38 C.

3. A method of preparing photographic emule I sions, comprising adding glass particles to the emulsion, exposing the emulsion to oscillations of approximately 100 meters wave length thus tending to producea development of heat, and main-' taining the temperature of the emulsion substantially constant by cooling at about 38 C.

4. A method of treating a photographic emulsion, comprising emulsifying, digesting and redigesting the emulsion at.38 C., submitting the emulsion to the action of an excess of oscillations of approximately 100 meters wave length thus tending to produce a substantial development of heat; and simultaneously maintaining the emul-' sion at38 C. by cooling with water at 15 C.

CARL ADOLF SCI-ILEUSSNER. 

